Doppler distortion in fullrange drivers - diyAudio
Go Back   Home > Forums > Loudspeakers > Full Range

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 24th May 2007, 10:16 AM   #1
diyAudio Member
 
Join Date: Oct 2005
Default Doppler distortion in fullrange drivers

It seems that a common perceived shortcoming of fullrange drivers is doppler distortion. The more I think about this, the more the common explanations worry me...

Please tell me where my logic fails:

Assume the situation where a single full range microphone is used to record a live performance. The microphone capsule will move back and forward under the influence of lower frequencies, while simultaneously moving under the influence of higher frequencies.

As the driver moves forward under the influence of a bass signal, higher frequencies will be artificially raised as the recording membrane is moving towards the signal source over time. Similarly, higher frequencies will be artificially lowered as the membrane moves away from the signal source over time.

So if we play this recording back using a fullrange driver in correct phase, doppler distortion will kick in. As the driver moves forward under the influence of bass, it will again raise higher frequencies artificially as the source moves towards the listener over time. Note that these frequencies have already been raised during the recording process described above.

But what happens if we run the fullrange driver out of phase with the microphone? The doppler distortion on the recording is cancelled out. The raising of high frequencies caused by the membrane moving toward the signal source during recording is undone when the loudspeaker moves away from the listener during playback!

The main point being, if a single capsule is used for recording mixed frequency audio; a single driver out of phase can reproduce the full audio range without doppler distortion.

C'mon: beat me down if my hypothesis is wrong!
  Reply With Quote
Old 24th May 2007, 10:33 AM   #2
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
Due to the smallish excursions of mic diaphragms Doppler distortion is a non-issue on the recording side.

It is however an issue on the reproduction side. Martin Colloms claims that it is an issue with fullrangers for excursions >3mm peak IIRC.

Your thesis has ben raised on this forum at least once so far.

Regards

Charles

Edit: Your thesis could be valid to a certain degree if both - the mic and the speaker - have exactly the same excursion, which is almost impossible to achieve.
  Reply With Quote
Old 24th May 2007, 10:55 AM   #3
Hartono is offline Hartono  Indonesia
diyAudio Member
 
Join Date: Nov 2002
Location: currently in China
"a single driver out of phase can reproduce the full audio range without doppler distortion"

Beat beat beat beat beat beat


if doppler distortion is really significant in loudspeaker
above approach is downright wrong.
  Reply With Quote
Old 24th May 2007, 10:58 AM   #4
Hartono is offline Hartono  Indonesia
diyAudio Member
 
Join Date: Nov 2002
Location: currently in China
ok where your logic fail is :

different size full range behave differently ( larger one have less excursion for same spl ).
  Reply With Quote
Old 24th May 2007, 11:05 AM   #5
diyAudio Member
 
Join Date: Oct 2005
Thanks phase-accurate,

I understand that the excursion of the capsule and driver would need to be identical for complete 'doppler distortion cancellation'.

The main point is that the combination of single capsule and single driver seems to be the best mechanism for avoiding doppler distortions. Most of the information available suggests that single drivers are more prone to this type of distortion, which is simply misleading.

Once you open up the discussion to considering how doppler effects are captured during recording, I would propose that the single driver is at worst still better than any 2, 3 or 4 way system.

Unless of course you have a system where you have multi-way microphone capsules mirroring the excursion of the drivers in multi-way speakers, which would seem even more difficult to achieve!

In the real world every disc is recorded differently using different numbers of different mics. No speaker system can ever account for these differences, so the minimalist in me says KISS :-)
  Reply With Quote
Old 24th May 2007, 12:59 PM   #6
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
Quote:
Once you open up the discussion to considering how doppler effects are captured during recording, I would propose that the single driver is at worst still better than any 2, 3 or 4 way system.
Quite the contrary is the case. Full-range drivers are always worse in this respect than multiway systems.
Maybe I wasn't clear enough: With the veeeeeeery small excursions of a mic diaphragm Doppler distortion will be negligible. Your fullranger will therefore not compensate for anything that isn't there in the first place. It will also cause more of it than any multiway system.

Regards

Charles
  Reply With Quote
Old 24th May 2007, 01:08 PM   #7
diyAudio Member
 
Join Date: Oct 2005
I see your point now - thanks for the lesson Charles!

My theory would only work if the speed of sound was reduced by the same factor as the difference in size of the mic capsule and drive unit - is this right?

Thanks guys - I'll stumble forwards less ignorant than before :-)
  Reply With Quote
Old 24th May 2007, 01:15 PM   #8
Hartono is offline Hartono  Indonesia
diyAudio Member
 
Join Date: Nov 2002
Location: currently in China
"My theory would only work if the speed of sound was reduced by the same factor as the difference in size of the mic capsule and drive unit - is this right?"

now this is tooooo much for me to chew
  Reply With Quote
Old 24th May 2007, 01:24 PM   #9
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
You might like to see what Mr Klipsch has to say about it. My website www.readresearch.co.uk in the articles section
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Fullrange Drivers From China! thetubeguy1954 Full Range 44 25th December 2009 10:44 AM
Where to buy Lyeco fullrange drivers??? kyrie48 Full Range 1 22nd November 2008 03:29 AM
IM and Doppler distortion in multi-way vs one-way systems. Nevod Multi-Way 4 27th September 2008 12:50 PM
Which sub to use with fullrange drivers ? Bubba Zanetti Subwoofers 11 2nd February 2008 09:36 PM


New To Site? Need Help?

All times are GMT. The time now is 07:35 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2